After reading this chapter, you should now have a good idea about DI design patterns, and the best practices for applying those patterns. Spring deals with the plumbing part, so, you can focus on solving the domain problem by using the dependency injection pattern. The DI pattern frees the object of the burden of resolving its dependencies. Your object is handed everything that it needs to work. The DI pattern simplifies your code, improves code reusability, and testability. It promotes programming to interfaces, and conceals the implementation details of dependencies. The DI pattern allows for centralized control over the object's life cycle. You can configure DI via two ways--explicit configuration and implicit configuration. Explicit configuration can be configured through XML-or Java-based configuration; it provides centralized configuration. But implicit configuration is based on annotations. Spring provides stereotype annotations for Annotation-based configuration. This configuration reduces the verbosity of code in the application, but it spreads out across the application files.

In the upcoming Chapter 5, Understanding the Bean Life Cycle and Used Patterns, we will explore the life cycle of the Spring bean in the container.